As is known, closing systems for doors of motor vehicles basically comprise a lock mounted on the door and a lock striker mounted in a fixed portion of the bodywork in the proximity of the opening of the door itself (or, more rarely, vice versa).
The lock comprises a closing mechanism designed to co-operate with the lock striker so as to obtain a relative blocking between the lock and the lock striker itself when the door is closed.
Currently, there is a widespread use of lock strikers of the type comprising a U-shaped element having opposite ends riveted onto a supporting plate. The U-shaped element is basically made up of two cylindrical portions, which extend orthogonally from the supporting plate and are radiused, on the opposite side, by a connecting portion set transverse to them.
The closing mechanism comprises a fork and a pawl which are hinged to respective pins fixed to a supporting body designed to be fixed to the door of the motor vehicle.
The fork is designed to couple in a releasable way with one of the cylindrical portions of the lock striker, hereinafter referred to as “engagement portion”, whilst the pawl is designed to block the fork, in a releasable way, in a position of closing on the lock striker.
In particular, the supporting body and the fork define respective U-shaped seats for housing and blocking the engagement portion of the lock striker. Each of said seats defines, at one end, an entry section for the engagement portion of the lock striker and is delimited, at an opposite end, by a bottom wall, which defines the position of arrest of said engagement portion.
The fork is pushed by a corresponding spring in the direction of an opening position, in which it presents the entry section of its own seat facing the same part of the entry section of the seat of the supporting body so as to enable introduction and extraction of the engagement portion of the lock striker in/from said seats. The said fork can be turned about its own pin in order to assume the aforesaid closing position, in which a portion of the side edge of the seat intercepts the seat of the supporting body so as to block the engagement portion of the lock striker within the seats themselves.
The pawl is designed to couple by snap action with the peripheral edge of the fork in order to block the fork itself, in a releasable way, in the closing position, and is loaded by a corresponding spring in the direction of said peripheral edge.
Typically, entry of the engagement portion of the lock striker into the seat of the supporting body is guided by the walls that delimit the seat itself at the sides, the said walls presenting a profile that converges in the direction of the bottom wall.
In order to reduce the noise produced by coupling between the lock striker and the lock, there are currently adopted constructional solutions based mainly upon the use of a buffer or damper, which is typically made of rubber and is set inside the seat of the supporting body and is coupled to the bottom wall of the seat itself so as to define a damped striking arrest for the engagement portion of the lock striker.
On account of the curvilinear conformation of the engagement portion of the lock striker, distribution of the contact pressures between the external surfaces of the engagement portion and of the buffer is not uniform. In particular, the contact pressure is maximum in an area corresponding to an intermediate portion of the buffer and decreases markedly towards the opposite side edges of the latter.
Over time, this may cause tearing of the buffer, with adverse effects on retention of the lock striker and on the damping action performed by the buffer. Furthermore, this phenomenon may cause an undesired increase in play between the dimensions of the door and the corresponding opening for receiving the door, which is provided in the bodywork of the motor vehicle, with consequent generation of noise and possible rattling of the door when the vehicle is travelling.